docs: def set(self, key, val):
      """Sets a value in a key.
  
      Args:
        key (str): Key for the value.
        val: Value to set.
  
      Returns:
        Retrieved value.
      """
      self._create_file_if_none_exists()
      with open(self.filename, 'r+b') as file_object:
        cache_pickle = pickle.load(file_object)
        cache_pickle[key] = val
        file_object.seek(0)
        pickle.dump(cache_pickle, file_object)